SHARP 20LK31M, 20LK61M Service Manual

20LK31M 20LK61M

SERVICE MANUAL

S80G420LK31M/

COLOR TELEVISION

Chassis No. SN-70A

20LK31M

In the interests of user-safety (Required by safety regulations in some countries) the set should be restored to its original condition and only parts identical to those specified should be used.

» ELECTRICAL SPECIFICATIONS.........................................................................................................1

» IMPORTANT SERVICE SAFETY PRECAUTION ................................................................................2

» LOCATION OF USER'S CONTROL.....................................................................................................4

» INSTALLATION AND SERVICE INSTRUCTIONS ...............................................................................5

» CHASSIS LAYOUT.............................................................................................................................10

» BLOCK DIAGRAM..............................................................................................................................12

» SCHEMATIC DIAGRAMS...................................................................................................................14

» PRINTED WIRING BOARD ASSEMBLIES........................................................................................21

» REPLACEMENT PARTS LIST ...........................................................................................................24

» PACKING OF THE SET......................................................................................................................31

20LK61M

MODELS

CONTENTS

20LK31M 20LK61M

Page

ELECTRICAL SPECIFICATIONS

POWER INPUT ........................................110-220 V AC 50/60 Hz

POWER RATING

20LK31M............................................................................ 88 W

20LK61M............................................................................ 98 W

PICTURE SIZE .......................................... 1,194cm2 (185sq inch)

CONVERGENCE ............................................................ Magnetic

SWEEP DEFLECTION.................................................... Magnetic

FOCUS .............................................. Hi-Bi-Potential Electrostatic

INTERMEDIATE FREQUENCIES

Picture IF Carrier Frequency .................................... 45.75 MHz

Sound IF Carrier Frequency..................................... 41.25 MHz

Color Sub-Carrier Frequency ................................... 42.17 MHz

(Nominal)

AUDIO POWER

OUTPUT RATING

20LK31M........................................... 1.5W (at 10% distortion)

20LK61M........................................... 3.0W (at 10% distortion)

SHARP CORPORATION

SPEAKER

SIZE ........................................................................ 9 cm × 5 cm

VOICE COIL IMPEDANCE

20LK31M ................................................... 16 ohm at 400 Hz

20LK61M ................................................... 32 ohm at 400 Hz

ANTENNA INPUT IMPEDANCE

VHF/UHF ................................................... 75 ohm Unbalanced

TUNING RANGES

VHF-Channels ............................................................. 2 thru 13

UHF-Channels ........................................................... 14 thru 69

CATV Channels ......................................................... 1 thru 125

Specifications are subject to change without prior notice.

20LK31M 20LK61M

IMPORT ANT SER VICE SAFETY PRECAUTION

Service work should be performed only by qualified service technicians who are throughly familiar with all safety checks and the servicing guidelines which follow:

WARNING

1. For continued safety, no modification of any circuit should be attempted.

2. Disconnect AC power before servicing.

3. Semiconductor heat sinks are potential shock hazards when the chassis is operating.

4. The chassis in this receiver has two ground systems which are separated by insulating material. The nonisolated (hot) ground system is for the B+ voltage regulator circuit and the horizontal output circuit. The isolated ground system is for the low B+ DC voltages and the secondary circuit of the high voltage transformer. To prevent electrical shock use an isolation transformer between the line cord and power receptacle, when servicing this chassis.

SERVICING OF HIGH VOL T AGE SYSTEM AND PICTURE TUBE

When servicing the high voltage system, remove the static charge by connecting a 10k ohm resistor in series with an insulated wire (such as a test probe) between the picture tube ground and the anode lead. (AC line cord should be disconnected from AC outlet.)

1. Picture tube in this receiver employs integral implosion protection.

2. Replace with tube of the same type number for continued safety.

3. Do not lift picture tube by the neck.

4. Handle the picture tube only when wearing shatterproof goggles and after discharging the high voltage anode completely.

X-RADIA TION AND HIGH VOL TAGE LIMITS

1. Be sure all service personnel are aware of the procedures and instructions covering X-radiation. The only potential source of X-ray in current solid state TV receivers is the picture tube. However, the picture tube does not emit measurable X-Ray radiation, if the high voltage is as specified in the "High Voltage Check" instructions. It is only when high voltage is excessive that Xradiation is capable of penetrating the shell of the picture tube including the lead in the glass material. The important precaution is to keep the high voltage below the maximum level specified.

2. It is essential that servicemen have available at all times an accurate high voltage meter. The calibration of this meter should be checked periodically.

3. High voltage should always be kept at the rated value

-no higher. Operation at higher voltages may cause a failure of the picture tube or high voltage circuitry and;also, under certain conditions, may produce radiation in exceeding of desirable levels.

4. When the high voltage regulator is operating properly there is no possibility of an X-radiation problem. Every time a color chassis is serviced, the brightness should be tested while monitoring the high voltage with a meter to be certain that the high voltage does not exceed the specified value and that it is regulating correctly.

5. Do not use a picture tube other than that specified or make unrecommended circuit modifications to the high voltage circuitry.

6. When trouble shooting and taking test measurements on a receiver with excessive high voltage, avoid being unnecessarily close to the receiver. Do not operate the receiver longer than is necessary to locate the cause of excessive voltage.

2 2

IMPORT ANT SER VICE SAFETY PRECAUTION

1.5k ohm 10W

0.15µF

TEST PROBE

CONNECT TO KNOWN EARTH GROUND

TO EXPOSED METAL PARTS

VOLTMETER

(Continued)

20LK31M 20LK61M

BEFORE RETURNING THE RECEIVER (Fire & Shock Hazard)

Before returning the receiver to the user, perform the following safety checks.

1. Inspect all lead dress to make certain that leads are not pinched or that hardware is not lodged between the chassis and other metal parts in the receiver.

2. Inspect all protective devices such as non-metallic control knobs, insulating materials, cabinet backs, adjustment and compartment covers or shields, isolation resistor-capacity networks, mechanical insulators and etc.

3. To be sure that no shock hazard exists, check for leakage current in the following manner.

» Plug the AC cord directly into a 120 volt AC outlet,

(Do not use an isolation transformer for this test).

» Using two clip leads, connect a 1.5k ohm, 10 watt

resistor paralleled by a 0.15mF capacitor in series with all exposed metal cabinet parts and a known earth ground, such as electrical conduit or electrical ground connected to earth ground.

» Use an AC voltmeter having with 5000 ohm per volt,

or higher, sensitivity to measure the AC voltage drop across the resistor.

» Connect the resistor connection to all exposed metal

parts having a return to the chassis (antenna, metal cabinet, screw heads, knobs and control shafts, escutcheon and etc.) and measure the AC voltage drop across the resistor. AII checks must be repeated with the AC line cord plug connection reversed. (If necessary, a nonpolarized adapter plug must be used only for the purpose of completing these check.) Any current measured must not exceed 0.5 milliamp. Any measurements not within the limits outlined above indicate of a potential shock hazard and corrective action must be taken before returning the instrument to the customer.

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SAFETY NOTICE

Many electrical and mechanical parts in television receivers have special safety-related characteristics. These characteristics are often not evident from visual inspection, nor can protection afforded by them be necessarily increased by using replacement components rated for higher voltage, wattage, etc. Replacement parts which have these special safety characteristics are identified in this manual; electrical components having such features are identified by "å" and shaded areas in the Replacement Parts Lists and Schematic Diagrams.

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For continued protection, replacement parts must be identical to those used in the original circuit. The use of substitute replacement parts which do not have the same safety characteristics as the factory recommended replacement parts shown in this service manual, may create shock, fire, X-radiation or other hazards.

20LK31M 20LK61M

Front Panel

LOCATION OF USER'S CONTROL

20LK61M20LK31M

POWER

Press → On. Press again → Off.

VOLUME UP/DOWN

(+) Increases sound. (–) Decreases sound.

SENSOR AREA FOR REMOTE CONTROL

CHANNEL UP/DOWN

) Selects next higher channel.

(

) Selects next lower channel.

(

Basic Remote Control Functions

POWER

Press → On. Press again → Off.

REMOTE KEYP AD

Accesses any channel from keypad.

FLASHBACK

Returns to previous channel.

VOLUME UP/DOWN

(+) Increases sound. (–) Decreases sound.

• In menu mode, changes or selects the TV adjustments.

VIDEO/AUDIOIN TERMINALS

POWER

Press → On. Press again → Off.

VOLUME UP/DOWN

(+) Increases sound. (–) Decreases sound.

SENSOR AREA FOR REMOTE CONTROL

Infrared Transmitter Window

INPUT

Press → Switch to external video input mode. Press again → Switch to TV mode.

CHANNEL UP/DOWN

) Selects next higher channel.

( (

) Selects next lower channel.

• Moves the “ screen.

” mark of the MENU

VIDEO/AUDIOIN TERMINALS

CHANNEL UP/DOWN

) Selects next higher channel.

(

) Selects next lower channel.

(

MUTE

Press Mutes sound. Press again → Restores sound.

• CLOSED CAPTION appears when sound is muted.

Press → Accesses MAIN MENU. Press again → Exits MAIN MENU.

DISPLAY

Press → Displays receiving channel for 4 seconds. Press again → Removes display .

• Temporarily displays receiving channel when in Closed Caption mode.

20LK31M 20LK61M

INSTALLATION AND SERVICE INSTRUCTIONS

Note: (1)When performing any adjustments to resistor controls and transformers use non-metallic

screwdrivers or TV alignment tools.

(2)Before performing adjustments, the TV set must be on at least 15 minutes.

CIRCUIT PROTECTION

The receiver is protected by a 4.0A fuse (F701), mounted on PWB-A, wired into one side of the AC line input.

X-RADIA TION PROTECTOR CIRCUIT TEST

After service has been performed on the horizontal deflection system, high voltage system, B+ system, test the X-Radiation protection circuit to ascertain proper operation as follows:

1. Apply 120V AC using a variac transformer for accurate input voltage.

2. Allow for warm up and adjust all customer controls for normal picture and sound.

3. Receive a good local channel.

4. Connect a digital voltmeter to TP653 and make sure that the voltmeter reads 21.3 ±1.5V.

5. Apply external 27.2V DC at TP653 by using an external DC supply, TV must be shut off.

6. To reset the protector , unplug the AC cord and make a short circuit between TP651 and TP652. Now make sure that normal picture appears on the screen.

7. If the operation of the horizontal oscillator does not stop in step 5, the circuit must be repaired before the set is returned to the customer.

HIGH VOL T AGE CHECK

High voltage is not adjustable but must be checked to verify that the receiver is operating within safe and efficient design limitations as specified checks should be as follows:

1. Connect an accurate high voltage meter between ground and anode of picture tube.

2. Operate receiver for at least 15 minutes at 120V AC line voltage, with a strong air signal or a properly tuned in test signal.

3. Enter the service mode and select the service adjustment "S03" and Bus data "01" (Y-mute on).

4. The voltage should be approximately, 26.0kV (at zero beam). If a correct reading cannot be obtained, check circuitry for malfunctioning components. After the voltage test, make Y-mute off to the normal mode.

20LK31M 20LK61M

For adjustments of this model, the bus data is converted to various analog signals by the D/A converter circuit.

Note: There are still a few analog adjustments in this series such as focus and master screen voltage. Follow

the steps below whenever the service adjusment is required.

To enter the service mode and exit service mode.

While pressing the Vol-up and Ch-up buttons at the sametime, plug the AC cord into a wall socket. Now, the TV set is switched on and enters the service mode. To exit the service mode, turn the television off by pressing the power button.

1. Service mode.

Before putting unit into the service mode, check that customer adjustments are in the normal mode. Use the reset function in the video adjustment menu to ensure customer control are in their proper (reset) position.

2. Service number selection.

In the service mode, you will see the window screen as window 1. There are 3 adjustment categories 2DEF, 3SIGNAL, 4FIX VALUE as show in Figure A.

Window 2: DEF

D01 D03 D05

RETURN

Window 4: FIX VALUE

RETURN NEXT

D02 D04 D06

Window 1: ADJUSTMENT Categories

F01 F02

F13 F14

DEF

SERVICE MODE

RETURN

SIGNAL

DEF SIGNAL FIX V ALUE EEPROM

FIX V ALUE

Window 3: SIGNAL

S01

S13 RETURN

F15 F16

F25 F26

RETURNPREVIOUS

S02 S12

RETURN

Figure A: Adjustment Categories

Press CH UP/DOWN button for selection and enter by VOL UP or VOL DOWN. Press CH UP/DOWN button to select the adjustment item and VOL UP/DOWN to adjust the data number for each categories.

(OSD disturbance can be erased by R/C display key) (Note: EEPROM – factory used only)

Below are the adjustments ranges and initial values for FIX VALUE category.

FIX V ALUE

SERVICE POSITION

F01 OPTION 1 00-FF B0 A0 F02 OPTION 2 00-FF 04 0C F03 E-SAVE 00-3F 23 1F F04 TUNER SETUP 00, 01 00 00 F05 R-TONE RD 00-7F 19 03 F06 R-TONE BD 00-7F 00 7C F07 B-TONE RD 00-7F 00 00 F08 B-TONE BD 00-7F 12 04 F09 FM LEVEL 00-1F 0C 0C F10 AFC GAIN 00, 01 00 00 F11 G DRIVE 00, 0F 00 0F F12 FBT BLK SW 00,01 01 01 F13 V COMP 00-07 07 07

ADJUST ITEM

RANGE

Below are the ranges and initial values for each adjustment and in each categories.

DATA

INITIAL VALUE

Table - A

(Hex)

SERVICE POSITION

F14 OSD CONT 00-03 02 01 F15 SHARPNESS 00-3F 19 19 F16 FLT SYS 00-07 00 00 F17 KILLER OP 00-07 04 02 F18 PRE SHOOT 00-03 03 00 F19 CORING 00-03 04 04 F20 DC REST 00-03 02 02 F21 BS START 00-03 01 01 F22 BS GAIN 00-03 01 01 F23 ABL START 00-07 00 00 F24 R/B ANGLE 00-0F 08 08 F25 H BLK R 00-0F 04 03 F26 H BLK L 00-0F 04 06

ADJUST ITEM

DEF

SERVICE

POSITION

D01 H-PHASE 00-1F 0C D02 V-SIZE 00-7F 40 D03 V-POSITION 00-3F 20 Must be "20" D04 CC-POSITION 00-FF 1A D05 V-LINEARITY 00-1F 10 Must be "12" D06 V-S-CORRECTION 00-1F 10 Must be "0F"

ADJUST ITEM

RANGE

DATA

INITIAL VALUE

ADJUSTMENT CONTENTS

RANGE

DATA

INITIAL VALUE

20LK31M 20LK61M

(Hex)

Table - B

SIGNAL

SERVICE

POSITION

S01 RF AGC 00-3F 14 S02 VIDEO LEVEL 00-07 03

S03 Y-MUTE 00-03 00 S04 SUB BIAS 00-FF 40 Must be "30"

S05 R-BIAS 00-FF 00 S06 G-BIAS 00-FF 00 S07 B-BIAS 00-7F 00 S08 R-DRIVE 00-7F 40 S09 B-DRIVE 00-7F 40 S10 CONTRAST 00-7F 5A S11 TINT 00-7F 40 S12 COLOR 00-7F 40 S13 BRIGHTNESS 00-7F 40

ADJUST ITEM

RANGE

Note: Refer to the SERVICE ADJUSTMENT for each corresponding values.

Holding down both the Vol-up/Ch-down buttons on the TV set at service mode for more than 2 seconds will automatically write the above initial values into IC2101.

PART REPLACED NOTES

NECESSARY UNNECESSARY

IC2001 IC201

IC2101

CRT

ADJUSTMENT

DATA

Table - C

INITIAL VALUE

ADJUSTMENT CONTENTS

"01":Y-MUTE, "02":V-STOP&Y-MUTE "03":Activate color killer circuit

Data is stored in IC2101. The adjustment is needed to compensate for characteristics

of parts including IC201. Holding down both the Vol-up/Ch-down buttons on the TV

set in the service mode for more than 2 seconds will automatically write the above initial values into IC2101.

Adjust items related to picture tube only.

Table - D

20LK31M 20LK61M

SERVICE ADJUSTMENT

RF AGC Adjustment

1. Receive a good local channel.

2. Enter the service mode signal category and select the service adjustment "S01".

3. Set the data value to point where no noise or beat appears.

4. Select another channel to confirm that no noise or beat appears.

Note: You have to exit the service mode first to

select another channel.

Video Level (TV Det Video Level) Adjustment

1. Receive a good local channel.

2. Enter the service mode signal category and select the service adjustment "S02".

3. Set the data value to "02" first, then adjust the data in ranges 02 ±2 step to obtain a normal contrast level.

Screen Adjustment

1. Connect to oscilloscope probe between TP855 and ground of the CRT unit.

2. Receive a good local channel.

3. Enter the service mode Signal category and set the service adjustment "S04" to step 30. Then select the service adjustment "S12" and set the data value to "00" to set the color level to the minimum level. (record the original data first). Y ou may skip this step, if you selected a B/W picture or monoscope pattern. Set also the "S05/S06/S07" data to minimum level.

4. Select the service adjustment "S03" and set the data value to "01" to turn off the luminance signal (Y -mute).

5. Select the service adjustment "S13" and adjust the data value to obtain 2.35 volts as shown in Figure B.

6. Adjust the master screen control until the raster darkens to the point where raster is barely seen.

7. Adjust the service adjustment "S05" red, "S06" green and "S07" blue to obtain a good grey scale with normal white at low brightness level.

8. Select the service a adjustment "S03" and reset data to "00". Select the service adjustment "S12" and reset data to obtain normal color level.

9. Remove probe and reset the master screen control to obtain normal brightness range.

White Balance Adjustment.

1. Receive a good local channel.

2. Select the service adjustment "S12" and set the data value to "00" to set the color level to the minimun. Y ou may skip this step, if you selected a B/W picture or monoscope.

3. Alternately adjust the service adjustment data of "S08" and "S09" until a good grey scale with normal white is obtained.

4. Select the service adjustment "S12" and reset data to obtain normal color level.

Sub-Picture Adjustment

1. Receive a good local channel.

2. Make sure the customer picture control is set to maximum.

3. Enter the service mode and select the service adjustment "S10".

4. Adjust the data value to achieve normal contrast range.

Sub-Tint Adjustment

1. Receive a good local channel.

2. Set the customer tint control to the center of it’s range.

3. Enter the service mode and select the service adjustment "S11".

4. Adjust "S11" data value to obtain normal fresh tones.

Sub-Color Adjustment

1. Receive a good local channel.

2. Make sure the customer color control is set to center position.

3. Enter the service mode and select the service adjustment "S12".

4. Adjust "S12" data value to obtain normal color level.

Sub-Brightness Adjustment

1. Receive a good local channel.

2. Make sure the customer brightness control is set to center position.

3. Enter the service mode and select the service adjustment "S13".

4. Adjust "S13" data value to obtain normal brightness level.

2.35 Vdc

GND

Figure B: Waveform for Screen Adjustment

20LK31M 20LK61M

Vertical-Size, V-Linearity and V-S Correction Adjustments

1. Receive a good local channel.

2. Enter the service mode DEF category and select the adjustment "D02" for Vertical Size, "D05" for VLinearity and "D06" for V-S Correction Adjustment.

3. Set in order "D05" for V-Linearity, "D06" for V-S Correction and set the data to get the best linearity.

4. Then adjust "D02" data unitl it become a proper vertical size.

Horizontal Position Adjustment

1. Receive a good local channel.

2. Enter the service mode DEF category and select the adjustment "D01".

3. Adjust "D01" data value to center the picture.

Vertical-Phase Adjustment

1. Receive a good local channel.

2. Enter the service mode DEF category and select the adjustment "D03".

3. Adjust "D03" bus data to get the most acceptable vertical position.

Note: The step range is 20 (032) ±10 steps.

Caption Position Adjustment (Horizontal)

1. Receive a good local channel.

2. Enter the service mode DEF category and select the adjustment "D04".

3. A black text box will appear on the screen. (see Figure C. below)

4. Adjust "D04" data value to balance the text box position in the center. (A=B).

A B

MTS ADJUSTMENT

MTS Level Adjustment

1. Feed the following monaural signal to pin (14) of IC3001. Monaural signal: 300Hz, 245mVrms

2. Connect the rms voltmeter to pin (39) of IC3001.

3. Enter the service mode and select the service adjustment "M01".

4. Adjust the data so that the rms voltmeter reads 490 ±10mVrms.

MTS VCO Adjustment

1. Keep the unit in no-signal state.

2. Connect the frequency counter to pin (39) of IC3001.

3. Connect a capacitor (100µF, 50V) in between positive(+) side of C3005 and ground.

4. Enter the service mode and select the service adjustment "M02"

5. Adjust the data so that the frequency counter reads

62.94 ±0.75kHz.

Filter Adjustment

1. Feed the following stereo pilot signal to pin (14) of IC3001 . Stereo pilot signal: 9.4kHz, 600mVrms.

2. Enter the service mode and select the service adjustment "M03".

3. Adjust the data at the point where "OK" appears on the screen. The "OK" represents the approximate center of the adjustable range of the data.

Separation Adjustment

1. Connect the rms voltmeter to pin (39) of IC3001.

2. Receive the following composite stereo signal 1. Composite stereo signal: 30% modulation, left channel only, noise reduction on, 300Hz

3. Enter the service mode and select the service adjustment "M04".

4. Adjust the data until the AC voltage reading of the rms voltmeter is minimum.

5. Receive the following composite stereo signal 2. Stereo signal: 30% modulation, left channel only, noise reduction on, 3kHz

6. Enter the service mode and select the service adjustment "M05".

7. Adjust the data until the AC voltage reading of the rms voltmeter is minimum.

8. Take the above steps 1 thru 7 again for fine adjustment.

Figure C.

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